Dynamic random-access memory

Dynamic random-access memory (DRAM) is a type of random access semiconductor memory that stores each bit of data in a separate tiny capacitor within an integrated circuit. The capacitor can either be charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. The electric charge on the capacitors slowly leaks off, so without intervention the data on the chip would soon be lost. To prevent this, DRAM requires an external memory refresh circuit which periodically rewrites the data in the capacitors, restoring them to their original charge. This refresh process is the defining characteristic of dynamic random-access memory, in contrast to static random-access memory (SRAM) which does not require data to be refreshed. Unlike flash memory, DRAM is volatile memory (vs. non-volatile memory), since it loses its data quickly when power is removed. However, DRAM does exhibit limited data remanence. Dynamic random-access memory (DRAM) is a type of random access semiconductor memory that stores each bit of data in a separate tiny capacitor within an integrated circuit. The capacitor can either be charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. The electric charge on the capacitors slowly leaks off, so without intervention the data on the chip would soon be lost. To prevent this, DRAM requires an external memory refresh circuit which periodically rewrites the data in the capacitors, restoring them to their original charge. This refresh process is the defining characteristic of dynamic random-access memory, in contrast to static random-access memory (SRAM) which does not require data to be refreshed. Unlike flash memory, DRAM is volatile memory (vs. non-volatile memory), since it loses its data quickly when power is removed. However, DRAM does exhibit limited data remanence. DRAM is widely used in digital electronics where low-cost and high-capacity memory is required. One of the largest applications for DRAM is the main memory (colloquially called the 'RAM') in modern computers and graphics cards (where the 'main memory' is called the graphics memory). It is also used in many portable devices and video game consoles. In contrast, SRAM, which is faster and more expensive than DRAM, is typically used where speed is of greater concern than cost and size, such as the cache memories in processors. Due to its need of a system to perform refreshing, DRAM has more complicated circuitry and timing requirements than SRAM, but it is much more widely used. The advantage of DRAM is the structural simplicity of its memory cells: only one transistor and a capacitor are required per bit, compared to four or six transistors in SRAM. This allows DRAM to reach very high densities, making DRAM much cheaper per bit. The transistors and capacitors used are extremely small; billions can fit on a single memory chip. Due to the dynamic nature of its memory cells, DRAM consumes relatively large amounts of power, with different ways for managing the power consumption. DRAM had a 47% increase in the price-per-bit in 2017, the largest jump in 30 years since the 45% percent jump in 1988, while in recent years the price has been going down. The cryptanalytic machine code-named 'Aquarius' used at Bletchley Park during World War II incorporated a hard-wired dynamic memory. Paper tape was read and the characters on it 'were remembered in a dynamic store. ... The store used a large bank of capacitors, which were either charged or not, a charged capacitor representing cross (1) and an uncharged capacitor dot (0). Since the charge gradually leaked away, a periodic pulse was applied to top up those still charged (hence the term 'dynamic')'. The Toshiba 'Toscal' BC-1411 electronic calculator, which was introduced in November 1965, used a form of capacitive DRAM (180 bit) built from discrete bipolar memory cells. The same year, Arnold Farber and Eugene Schlig, working for IBM, created a hard-wired memory cell, using a transistor gate and tunnel diode latch. They replaced the latch with two transistors and two resistors, a configuration that became known as the Farber-Schlig cell. In 1965, Benjamin Agusta and his team at IBM created a 16-bit silicon memory chip based on the Farber-Schlig cell, with 80 transistors, 64 resistors, and 4 diodes. The earliest forms of DRAM mentioned above used bipolar transistors. While it offered improved performance over magnetic-core memory, bipolar DRAM could not compete with the lower price of the then dominant magnetic-core memory. Capacitors had also been used for earlier memory schemes, such as the drum of the Atanasoff–Berry Computer, the Williams tube and the Selectron tube. The invention of the MOSFET (metal-oxide-semiconductor field-effect transistor), also known as the MOS transistor, at Bell Labs in 1959, led to the development of MOS (metal-oxide-semiconductor) DRAM. The first MOS DRAM was developed by Dr. Robert Dennard at the IBM Thomas J. Watson Research Center in 1966. He was granted U.S. patent number 3,387,286 in 1968. MOS memory offered higher performance, was cheaper, and consumed less power, than magnetic-core memory. MOS DRAM chips were commercialized in 1969 by Advanced Memory system, Inc of Sunnyvale, CA. This 1000 bit chip was sold to Honeywell, Raytheon, Wang Computer, and others.The same year, Honeywell asked Intel to make a DRAM using a three-transistor cell that they had developed. This became the Intel 1102 in early 1970. However, the 1102 had many problems, prompting Intel to begin work on their own improved design, in secrecy to avoid conflict with Honeywell. This became the first commercially available DRAM, the Intel 1103, in October 1970, despite initial problems with low yield until the fifth revision of the masks. The 1103 was designed by Joel Karp and laid out by Pat Earhart. The masks were cut by Barbara Maness and Judy Garcia. MOS memory overtook magnetic-core memory as the dominant memory technology in the early 1970s.